The aforesaid U.S. Pat. No. 5,002,023 specifically illustrates and describes a hydraulically operated VCT system in which the operating hydraulic fluid is engine lubricating oil and in which the camshaft(s) is (are) driven by a timing chain which is continuously lubricated by the engine lubricating oil to ensure proper operation of the chain and its associated components. However, many engine types utilize cogged timing belts in transmitting torque from a crankshaft to the camshaft(s) of a single camshaft or multiple camshaft engine, and such belt driven systems are usually operated in a dry or unlubricated condition. Thus, to adapt a VCT system of the aforesaid U.S. Pat. No. 5,002,023 to a timing belt driven engine, it is desirable that appropriate seals be utilized to prevent engine lubricating oil from contacting the belt(s) and the associated pulleys and other components which regularly contact the belt(s) during the operation of the engine.
Further, the use of the hydraulically operated control system of the aforesaid Ser. No. 713,465 to control the positioning of a spool in the hydraulic circuitry of the VCT actuating vane pump and related hydraulic circuitry would introduce substantial complexity into the design of the control system and the environment around it to suitably seal the control system and thereby ensure the proper, dry operation of the timing belt(s) and associated components. In the present invention, this can be accomplished by using a linearly acting electric motor, such as a stepper motor, to position the spool of the VCT control system spool valve.